The overall hypothesis is that caveolin-1 (cav-1) interacts with vascular endothelial growth factor (VEGF) receptors (VEGFR) directly and/or indirectly to concentrate VEGFR initiated signaling events, i.e., Ras-Raf-MEK1-ERK2/1 and PI3K/Akt signaling modules, in the caveolae of endothelial cells (EC), thereby modulating VEGF regulation of EC proliferation, migration, and differentiation. Moreover, cav-1/caveolae may regulate placental angiogenesis by modifying the bioavailability of nitric oxide (NO) in EC. To address this hypothesis, an ovine fetoplacental artery EC model and a human placental capillary endothelial cell line will be used. Specific Aim 1: To further clarify if VEGFRs (i.e., KDR, Flt-1, and NP-1) are physically associated with cav-1 in vitro and in vivo, thus localized in the caveolae, and if overexpression of exogenous cav-1 or targeted down-regulation of endogenous cav-1 regulates ligand-dependent VEGFR activation. Specific Aim 2: To determine if targeted down-regulation of endogenous cav-1 or overexpression of exogenous cav-1 alters VEGF stimulation of cell cycle entry, proliferation, migration and differentiation. Specific Aim 3: To determine if VEGF activates the Ras/Raf/ERK2/1 and PI3K/Akt signaling modules in the caveolae. Specific Aim 4: To delineate if down-regulation of cav-1 or cav-1 overexpression modulates VEGF stimulation of MAPK and PI3K/Akt signaling pathways and the role of these pathways in VEGF-induced cell cycle entry, cell proliferation, migration, and differentiation. Specific Aim 5: To determine if targeted down-regulation of endogenous cav-1 or overexpresison of exogenous cav-1 alters eNOS activity thereby altering the bioavaibility Iof NO, which in turn regulates placental angiogenesis. These studies will have a great impact on our understanding of caveoli, VEGF/VEGFR, endothelial, and angiogenesis biology, all are biologically important fields we have integrated in the proposal clinically relevant to placental angiogenesis and vasodilatation for the first time. The ultimate clinical importance of this research is evident when one considers that uteroplacental endothelial adaptations to pregnancy, especially the rises in fetoplacental and uteroplacental perfusion, are linked directly to fetal growth and survivability and that these mechanisms are dysfunctional in pathologic pregnancies such as preeclampsia and IUGR.